5.1 Process considerations when coating maintenance may be performed
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Statutory Documents - IMO Publications and Documents - Circulars - Maritime Safety Committee - MSC.1/Circular.1399 – Guildelines on Procedures for In-Service Maintenance and Repair of Coating Systems for Cargo Oil Tanks of Crude Oil Tankers – (10 June 2011) - Annex – Guidelines for Maintenance and Repair of Protective Coatings for Cargo Oil Tanks of Crude Oil Tankers - 5 Coating Maintenance - 5.1 Process considerations when coating maintenance may be performed

5.1 Process considerations when coating maintenance may be performed

  5.1.1 The following considerations should be taken into account when coating maintenance is undertaken:

  • .1 safety, including tank entry requirements;

  • .2 tank surface cleaning;

  • .3 salt contamination;

  • .4 rust scale;

  • .5 pitting corrosion;

  • .6 temperature;

  • .7 condensation;

  • .8 ventilation; and

  • .9 compatibility of coating systems.

  5.1.2 Safety. Refer to the Recommendations for entering enclosed spaces aboard ships (resolution A.864(20)), as amended, and ISGOTTfootnote. It is an absolute requirement that all of the ship's safety and tank entry procedures and policies are adhered to. All risks for the entry into tanks should be taken into account. In addition, it is strongly recommended that all travel coating squad members are trained in safe usage of all the equipment and tools to be used for the project on board, before being sent to the ship.

  5.1.3 Tank and surface cleaning. Inadequate tank and surface cleaning, may leave a few microns of oil film thickness on the surface which will seriously affect any coating attachment and will shorten the effective life of the maintenance undertaken – see paragraph 6.1.3.

  5.1.4 Salt contamination will cause accelerated deterioration of the maintenance coating if not removed prior to coating application. A recommended procedure to reduce salt contamination is to remove corrosion products including rust and black scale before washing the steel surface with fresh water. This should be the starting point in any surface preparation process in cargo tanks on board ships.

  5.1.5 Rust scale that is not removed prior to coating application will cause early failure. Loose top-scale is easy to remove, however the inner (black) hard scale is much more adherent. When over-coated it will soon detach between the steel and the scale and come off, typically with the coating adhering very well to the outside of it. If the hard scale is not removed, the service life expectancy of the treatment is maximum 1 to 2 years regardless of the coating used.

  5.1.6 Pitting corrosion is a common problem in unprotected areas of cargo tanks that have been exposed to crude oil for some time. If it has been accepted that the pits need not be welded up, in order to prevent further accelerated damage, a coating should be applied. Soluble salts will be present within the pits and it is essential that these are removed otherwise corrosion will soon start inside over-coated pits, affecting the service life. As salt contamination is concentrated in pits the use of ISO 8502-6 and ISO 8502-9 may result in misleading results. Various methods of salt removal from pits have been proposed for long term repair, however, for shipboard maintenance purpose, high pressure fresh water washing is recommended.

  5.1.7 Temperature is a critical parameter to consider. When trading in cold water, the risk of condensation is increased and the curing of two-component paints such as epoxy paints is retarded. Plan, if possible, the maintenance operation for periods, or locations, of warmer water. Otherwise lowering ballast water in side and double-bottom tanks to avoid contact with the back side of plating to be treated is recommended.

  5.1.8 Condensation is always a risk on board ships. It is advisable that the crew have a good understanding about relative humidity and its relation to substrate temperature and dew point. A coating applied over a surface that is at or below the dew point, or that will be at or below the dew point while the coating is still curing, will not perform. Ideally the temperature should be at least 3°C above the dew point.

  5.1.9 Ventilation is a vital factor for safety and quality of the coating application and must be carried out continuously during surface preparation, paint application, drying and curing. Ventilation arrangements must provide maximum efficiency, e.g., by arranging the ventilation so it extracts from the lowest and furthest corners to ensure the fast and efficient removal of solvents. The use of solvent free coating systems eliminates solvent release from the paint, but ventilation is still required during surface preparation and curing.

  5.1.10 Compatibility of coating systems is of utmost importance for a good end result. To ensure compatibility of coating systems, using the same coating system as was originally employed is recommended. If this is not possible, the coating manufacturer recommendations should be followed. When applying touch up, the intact coat next to the damaged area should be feathered for good adhesion.

Parent topic: 5 Coating Maintenance
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